The principal objective is to develop improved and optimized methods of cyclic external pneumatic compression (EPC) of the leg for the prevention of deep venous thrombosis. The current devices and pressure cycles for EPC are based on an unproven assumption, namely, that the controlling factor for minimizing thrombus formation is complete emptying in each pressure cycle. Alternate factors might be (a) high volume flow rate (ml/min); (b) high blood speed (cm/min); (c) high acceleration; and (d) high shear stress. Current EPC methods are far from optimal with respect to these parameters. This proposal is for collaborative research at Massachusetts Institute of Technology (M.I.T.) and Massachusetts General Hospital (M.G.H.) involving: (1) biomedical engineering studies of venous hemodynamics when EPC is applied; and (2) related physiologic studies on normal and diseased patients, on patients undergoing elective surgery, and on freshly-amputated legs. If the results of this proposal show that alternate EPC methods (e.g., (1) longitudinally-moving waves of compression by means of segmented boots or cuffs; or (2) high-frequency compression with small volume discharge per cycle) are significantly superior to the current EPC technique with regard to factors (a), (b), (c), (d) above, a subsequent follow-up proposal will be submitted jointly by M.G.H., Beth Israel Hospital, and M.I.T. for clinical trials of the alternate method on neurosurgical patients, on patients receiving total hip replacement surgery, and on other high-risk patients.